[DirectWrite] Disable subpixel font positioning if AA is disabled

DirectWrite with subpixel font positioning renders really badly when
font smoothing has been completely disabled.

Change FontPlatformData::setupPaint to gate subpixel positioning on the
precense of some type of font smoothing, be it standard or ClearType.

BUG=383372
R=cpu@chromium.org

Review URL: https://codereview.chromium.org/357383002

git-svn-id: svn://svn.chromium.org/blink/trunk@177251 bbb929c8-8fbe-4397-9dbb-9b2b20218538